Here is my use of my 3 way.
Before the trip I start the fridge on 120v at home.
I have a frozen gallon of water plus a half gallon.
They go in first.The food kept in the 3 way is frozen to start with.
All is loaded and when leaving change over to propane.
I keep it on propane usually wile driving.
In camp it's always on propane and the contents stay frozen.
The frozen water jugs help to keep the temp at or below freezing.
I have seen temps in the fridge as low as 28*
Our day to day cold items are kept in a 45L Truckfridge brand of cooler which runs all the time.
This uses very little power and the solar keeps up without any problem.
We have used this method for our cold storage items since we have had the camper.
We are more or less vegetarian maybe some salmon and chicken but that keeps well frozen.
This has worked very well for us.Our trips a lot of time are 3/4 weeks out.
We have taken two long trips to Alaska with ferry time
and the frozen items in the 3 way with the frozen water jugs has worked well.
The Truckfridge will run on our 100a battery for about 5 days without being charged.
This is our method ,I would like to hear others also.
Frank